1. Field of the Invention
The present invention relates to a resist composition and a patterning process using the resist composition. The resist composition comprises, as the base resin, a combination of at least two polymers which contain at least one type of acid labile group and are crosslinked within a molecule and/or between molecules with crosslinking groups having C--O--C linkages. This resist composition provides a much improved alkali dissolution contrast before and after exposure, high sensitivity, and high resolution. In particular, it has an excellent reproducibility as a micropatterning material for VLSI fabrication.
2. Prior Art
Deep-ultraviolet lithography, one of a number of recent efforts that are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, is thought to hold particular promise as the next generation in microfabrication technology. Deep-UV lithography is capable of achieving a minimum feature size of 0.5 .mu.m or less and, when a resist having low light absorption is used, can form patterns with sidewalls that are nearly perpendicular to the substrate.
Recently developed acid-catalyzed chemically amplified positive resists, such as those described in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619, utilize a high-intensity KrF excimer laser as the deep-UV light source. These resists, with their excellent properties such as high sensitivity, high resolution, and good dry etching resistance, are especially promising for deep-UV lithography.
Chemically amplified positive resists such as this include two-component systems comprising a base resin and a photoacid generator, and three-component systems comprising a base resin, a photoacid generator, and a dissolution regulator having acid labile groups.
For example, JP-A 115440/1987 describes a resist comprising poly-4-tert-butoxystyrene and a photoacid generator, and JP-A 223858/1991 describes a similar two-component resist comprising a resin bearing tert-butoxy groups within the molecule, in combination with a photoacid generator. JP-A 211258/1992 describes a two-component resist which is comprised of polyhydroxystyrene bearing methyl, isopropyl, tert-butyl, tetrahydropyranyl, and trimethylsilyl groups, together with a photoacid generator.
JP-A 100488/1994 discloses a resist comprised of a polydihydroxystyrene derivative, such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene] or poly[3,5-bis(2-tetrahydropyranyloxy)styrene], and a photoacid generator.
However, when the base resin in these resists bears acid labile groups on side chains and these acid labile groups are groups such as tert-butyl and tert-butoxycarbonyl which are cleaved by strong acids, the resin reacts with air-borne basic compounds and loses some of its activity, as a result of which cleavage of the acid labile groups arises less readily and the resist pattern tends to take on a T-top profile. By contrast, alkoxyalkyl groups such as ethoxyethyl are cleaved by weak acids, and so are little affected by air-borne basic compounds. Yet, their use also has its drawbacks, such as considerable narrowing of the pattern configuration as the time interval between exposure and heat treatment increases. Moreover, the presence of bulky groups on the side chains lowers the thermal stability of the resin, making it impossible to achieve a satisfactory sensitivity and resolution. These problems have hitherto prevented the practical implementation of either approach, and workable solutions have been sought.
The polymers described in JP-A 305025/1996 represent an attempt to resolve the foregoing problems, but characteristics of the production process render difficult the design of substituent ratios for acid labile groups and crosslinking groups. An additional shortcoming is that the production of these compounds results in the incidental formation of the crosslinking groups mentioned in JP-A 253534/1996. That is, in the design of resist compositions, polymers having various alkali dissolution rates are required, depending on the types and amounts of photoacid generators and additives selected, in addition to which the production of these polymers must be a reproducible process. However, the production methods described in the above prior-art references are subject to inherent limitations in the selection of acid labile groups and crosslinking groups, and in their substituent ratios.